Abstract

Despite its high capacity to take up nitrate from soil, winter rapeseed (Brassica napus) is characterized by a low N recovery in seeds. Thus, to maintain yield, rapeseed requires a high fertilization rate. Increasing nutrient use efficiency in rapeseed by addition of a biostimulant could help improve its agroenvironmental balance. The effects of marine brown seaweed Ascophyllum nodosum on plant growth have been well described physiologically. However, to our knowledge, no study has focused on transcriptomic analyses to determine metabolic targets of these extracts. A preliminary screening of different extracts revealed a significant effect of one of them (AZAL5) on rapeseed root (+102 %) and shoot (+23 %) growth. Microarray analysis was then used on AZAL5-treated or nontreated plants to characterize changes in gene expression that were further supported by physiological evidence. Stimulation of nitrogen uptake (+21 and +115 % in shoots and roots, respectively) and assimilation was increased in a similar manner to growth, whereas sulfate content (+63 and +133 % in shoots and roots, respectively) was more strongly stimulated leading to sulfate accumulation. Among the identified genes whose expression was affected by AZAL5, MinE, a plastid division regulator, was the most strongly affected. Its effect was supported by microscopic analysis showing an enhancement of chloroplast number per cell and starch content but without a significant difference in net photosynthetic rate. In conclusion, it is suggested that AZAL5, which promotes plant growth and nutrient uptake, could be used as a supplementary tool to improve rapeseed agroenvironmental balance.

Notes

Acknowledgments

This study was part of the AZOSTIMER project, selected and supported by the Pôle de compétitivité Mer-Bretagne, and funded by French FUI (Fond Unique Interministériel), Brittany Region and Saint-Malo Agglomeration. The authors thank Marie-Paule Bataillé and Raphaël Ségura for IRMS analyses and Angel-Mari Zamarreño for analyses of phytohormones. The authors acknowledge Patrick Beauclair for LICOR measurement, Julie Levallois for technical assistance in RNA extractions and q-PCR analyses, Xavier Sarda and Anne-Françoise Ameline for helping with plant culture and harvest, and finally Nicolas Elie from GRECAN (Groupe Régional d’Etude sur le CANcer, Histo-imagerie quantitative, Caen, France) for microscopy image analyses. The authors thank Laurence Cantrill for improving the English of the manuscript.